The invention relates to a device for transferring high voltage between two parts which are rotatable relative to each other. Each of the two parts comprises an insulator body. At least one of the parts comprises an electrode arrangement which carries the high voltage. The electrode is concentric with the axis of rotation and is in electrical contact with contact elements. A device of this kind is required, for example, for high voltage transfer in a computer tomography X-ray apparatus.
German Offenlegungsschrift No. 3010819 discloses a high voltage transfer device in which, the rotating part comprises an electrode track. The electrode track is concentric with the axis of rotation contact elements, which are mounted on the stationary part of the device and which are connected to the high voltage generator, slide on the electrode track. In order to increase the creepage path between an electrode arrangement and ground or between electrode arrangements carrying different high voltage potentials, the rotor and the stator comprise engaging ridges which are concentric with the axis of rotation.
The field distribution at the area of the electrode track is substantially inhomogeneous. The maximum of the field occurs directly at the surface of the electrode track, at least a part of which is in contact with air. Consequently, the air is liable to be ionized. This may damage the insulator bodies.
Another high voltage transfer device is described in United Kingdom Patent Application No. 2,061,028. In this device, the space between the rotor and the stator is filled with an electrically insulating liquid, for example oil, which has a substantially higher breakdown voltage than air. However, seals must be provided between the two parts which are rotatable relative to each other in order to prevent leakage of the liquid.
Still another high voltage transfer device is described in European Patent Application No. 39,994. In this device, however, the space between the rotor and the stator is filled with a gas having a substantially higher breakdown voltage than air. The gas may be, for example, sulphur hexafluoride or "Freon". The contact elements are constructed as contact brushes surrounded by a screen which serves to reduce the field strength at the area of the contact brushes.
All known devices have in common a substantially inhomogeneous field distribution at the area of the electrode track, with a maximum field strength at the electrode surface. The contact elements must be shaped so that the field strength does not become excessively high. Wear particles formed during the sliding of the contact elements on the electrode track contaminate the insulator surface in the direct vicinity of the electrode track or the electrode track itself, so that the electric strength of the device is reduced.